High-resolution digital phase modulator for a fiber optic signal transmission or measurement device

ABSTRACT

A digital phase modulator for a fiber-optic measurement device. A predetermined total number of electrodes of different lengths are arranged in parallel and on both sides of a light guidance path in or on an optical substrate. The electrodes are arranged in two or more triples along the light guidance path. In each case, two electrodes of successive length within a triple have the same length ratio with respect to one another. Such length ratio is chosen, in particular, to be ν=1.618. The electrode lengths of this triple are chosen such that the smallest step widths of the output value range of the phase modulator can be formed by subtraction between the values of at least two larger electrodes. This allows the resolution of the phase modulator to be increased from 9 bits to 11 bits without change in chip size.

BACKGROUND

1. Field of the Invention

The present invention relates to digital phase modulators. Moreparticularly, the invention pertains to a digital phase modulator for afiber-optic signal transmission or measurement device of the type thatincludes a fixed number of electrodes of different lengths arranged inparallel and on both sides of a light guidance path in or on an opticalsubstrate.

2. Description of the Prior Art

It is known to apply the same potentials to the electrodes of a phasemodulator for drive purposes. The potentials result in a positive ornegative shift in the light phase at the output of the modulatordepending on the positions of the electrodes with respect to the lightguidance path. (Electrodes are also referred to as “positive” and“negative” electrodes.)

Patent specification DE 197 53 427 C1 discloses a low-significancecomponent of a binary drive signal, supplied via a digital/analogconverter with a downstream driver, to a specific, separate analogelectrode in an otherwise digital phase modulator. This increases theaccuracy of the phase modulator, which is formed from binary-weightedflat electrodes, for a fiber-optic signal transmission or measurementdevice (preferably for a fiber-optic interferometer). The patentspecification also teaches storing correction values, which can beassociated individually with the electrodes of the phase modulator, in amemory table to correct production-dependent inaccuracies in theelectrode lengths and areas, and, thus, the phase modulation values.This solution increases resolution at the cost of comparatively largetechnical complexity that results from the need to use a D/A converterwith a driver, whose analog initial values are, of limited temperaturestability. When using such a phase modulator in a fiber-optic gyroscope(FOGs) with closed control loop comprising restoration electronics thatproduces a digital restoration signal of relatively high resolution(e.g. a 12-bit signal) for gyroscope restoration and for otherfiber-optic signal-transmission and measurement devices, it is desirablethat the resolution of the digital phase modulator exceed thatpreviously possible.

One problem in the production of digitally driven integrated-opticalmodulators (e.g. for FOGs implemented in a multifunctionalintegrated-optical chip (MIOC)) is the achievable and/or reproducibleresolution of electrode lengths. Based on voltage U_(|) and a minimumlength of the least significant (LSB) electrode of about 40 μm, anoverall electrode length of about 10 mm is required for a 9-bitconverter that can be relatively well implemented. If one were toattempt to reduce the minimum length of the LSB electrode further,considerable inaccuracies would occur as a result of field distortion.Relative accuracy of the LSB value could not be achieved, due toproduction tolerances. An electrode length of 80 mm would be requiredfor a 12-bit converter. Based on such requirements for U_(|) and the LSBlength of the shortest electrode this is neither feasible nor realisticdue to the considerable increase in physical length. Overall modulatorlength is limited to a few centimeters due to the technologicalconstraints mentioned above and others.

SUMMARY AND OBJECTS OF THE INVENTION

It is therefore an object of the present invention to provide a digitalphase modulator for a fiber-optic signal-transmission or measurementdevice, of considerably increased resolution without increased physicallength.

The present invention addresses the receding and other objects byproviding, in a first aspect, a digital phase modulator for afiber-optic signal transmission or measurement device. Such phasemodulator has a predetermined total number of electrodes of differentlengths arranged in parallel on both sides of a light guidance path inor on an optical substrate. Preferably identical control potentials canbe applied to the electrodes on both sides of the light guidance path insuch a way that a large number of phase valves can be set by changingthe drive selection of electrode combinations within a predeterminedvalue range.

The electrodes of the phase modulator are arranged in two or moretriples along the light guidance path. In each case, two electrodes ofsuccessive length of a triple have the same length ratio ν with respectto one another.

In a second aspect, the invention provides a digital phase modulator ofthe type described in the first paragraph of the first aspect of theinvention in which the electrodes are arranged in two or more triplesalong the light guidance path. In each case, two electrodes ofsuccessive length within a triple are of the same length ratio withrespect to one another within one triple from the second to the mostsignificant (MSB) triple. The electrode lengths of the first, leastsignificant (LSB) triple are chosen such that the smallest step widthsof the output value range of the phase modulator can be formed bysubtraction between the values of at least two larger electrodes.

The preceding and other features of the invention will become furtherapparent from the detailed description that follows. Such description isaccompanied by a set of drawing figures. Numerals of the drawingfigures, corresponding to those of the written description, point to thefeatures of the invention with like numerals referring to like featuresthroughout both the drawing figures and the written description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram that illustrates a subdivision and arrangement ofthe electrodes in a non-binary phase modulator in accordance with theinvention;

FIG. 2 is a diagram of the layout of an integrated-optical chipillustrated as a subsection of an MIOC of a fiber-optic gyroscopefollowing a beam splitter (Y splitter);

FIG. 3 is a block diagram of a basic arrangement for electroniccorrection or conversion of binary values to non-binary values forapplication to the individual electrodes in a phase modulator inaccordance with the invention;

FIG. 4 is a block diagram, corresponding to that illustrated in FIG. 3,of the layout of a correction table with an external correctioncapability; and

FIG. 5 is a modified block diagram layout of the circuit arrangement ofFIG. 3, which permits selective switching between two or more correctiontables stored in a memory.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 is a schematic diagram that illustrates the basic design of adigital phase modulator in accordance with the invention. A detailedsection of an electrode triple with the two shorter electrodes A, B isshown on the left-hand side with the largest electrode C shown on theright-hand side, to assist identification of a light guidance path L(indicated schematically) within the substrate of the MIOC (not shown inFIG. 1).

In accordance with the first fundamental concept of the invention, twoelectrodes of successive size have the same size ratio ν with respect toone another. This results in the following relationship, using theelectrode values a, b, c for the electrodes A, B, C: $\begin{matrix}{{\frac{b}{a} = {\frac{c}{b} = \nu}}{c = {a + b}}} & \left( {{Equation}\quad 1} \right)\end{matrix}$it follows that:c=ν ² ·a1=ν²−ν  (Equation 2)so that the size ratio ν is: $\begin{matrix}{\nu = {\frac{1}{2} + {\sqrt{\frac{5}{4}}{1.618.}}}} & \left( {{Equation}\quad 3} \right)\end{matrix}$If the values a₁, b₁, c₁ . . . a₄, b₄, c₄ (see the following list) areassigned to the electrodes E0 to E11 (contained in the four electrodetriples 1 to 4 of FIG. 1) within a triple then, observing the aboverequirement, this results, for example, in the condition a₂=ν·c₁.

The power series l, ν, ν², ν³ . . . that results must also be multipliedby the mathematical sign of the field strength direction within thephase modulator. For example, the electrodes on the right-hand side inFIG. 1 (i.e. the electrode C in the detailed section) each act on thephase of the light with an opposite mathematical sign to that of theelectrodes A, B on the other side of the light guidance path L. TABLE 1Value list for electrodes (see FIG. 1) Value allocation Electrodes inthe triple E0 a₁ E1 b₁ E2 c₁ E3 a₂ E4 b₂ E5 c₂ E6 a₃ E7 b₃ E8 c₃ E9 a₄E10 b₄ E11 c₄

This results in the weights or value sequences listed in Table 2: TABLE2 Value sequence 1 1.00 ν 1.62 — ν² −2.62 ν³ 4.23 ν⁴ 6.85 — ν⁵ −11.09 ν⁶17.94 ν⁷ 29.03 — ν⁸ −46.97 ν⁹ 75.99 ν¹⁰ 122.96 — ν¹¹ −198.96

The initial condition (Equation 1) implies that all of the combinationsa+b+c=0 disappear. This results in seven different output values foreach electrode triple. Twelve different states result for four electrodetriples, as identical combinations occur due to the relationshipν³=ν²+n. The length ratio between the longest and the shortest electrodeis 1:259.

The condition a+b=c (Equation 1) for opposed electrodes limits themaximum number of output values that can be described by 12 bitsindependent of the length ratios of the triples with respect to oneanother. Since a zero is produced with two different bit combinations[000] and [111] in each triple, seven different values can berepresented. For the four electrode triples 1 to 4 shown in FIG. 1, thisresults in 7⁴=2041 values (i.e., is to say a resolution of approximately±10 bits).

The second basic embodiment of the invention is based on the electrodeconfiguration and subdivision shown in FIG. 1. That is, it is also basedon the non-binary 1.618 configuration. It differs by avoiding valuerange overlaps between individual electrode triples.

To satisfy this leads to Equation 4 below. Such equation states that thesmallest electrode in a triple should be larger by a unit step width |1|than the sum of the lengths of all the smaller electrode triples. Thatis, $\begin{matrix}{a_{x} = {l_{x,0} = {{\left( {\sum\limits_{i = 0}^{x - 1}\left( {\sum\limits_{j = 0}^{2}{l_{i,j}}} \right)} \right) + {1\quad{for}\quad x}} \in \left\{ {1,2,3} \right\}}}} & \left( {{Equation}\quad 4} \right)\end{matrix}$The variable l_(i,j) denotes the electrode lengths, with

-   -   the index “i” denoting the triple number {0, 1, 2, 3 . . . },        and    -   the index “j” indicating the number of the electrode in the        respective triple {0, 1, 2}.        In other words, “l_(i,j)” thus represents the length of the j-th        electrode of the i-th triple.

The length of the respective central electrode b_(x) is twice that ofa_(x), i.e., b_(x)=2 a_(x). The largest electrode length c_(x) within atriple is given by the sum of a_(x) and b_(x) (c_(x)=a_(x)+b_(x)).

The resultant bit weights are summarized, by way of example, in Table 4,below. The association between the electrode designations l and thetriple-internal electrode designations a, b, c is employed to betterillustrate the situation and to avoid double indexing for the positionassociation. TABLE 4 Value sequence with the approach according toEquation 4 Variable Position Value l_(0.0) a₀ 1 l_(0.1) b₀ 2 l_(0.2) c₀−3 l_(1.0) a₁ 7 l_(1.1) b₁ 14 l_(1.2) c₁ −21 l_(2.0) a₂ 49 l_(2.1) b₂ 98l_(2.2) c₂ −147 l_(3.0) a₃ 343 l_(3.1) b₃ 686 l_(3.2) c₃ −1029The size ratio between the LSB and MSB combination is, in this case,1:1029. The totality of the bit combinations shown in Table 4 results in2400 different output values. The maximum possible number of outputvalues for this electrode configuration is therefore considerablygreater than for the first embodiment of the invention.

The magnitudes of the intervals between adjacent values are “0” or “1”.No other intervals occur with this distribution. Resolution is thusabout eleven (11) bits for the value range covered.

To further improve the size ratio between the longest and shortestelectrodes in accordance with the above, the electrodes in the LSBtriple 1 may be enlarged on the basis of Table 4. This is illustrated byway of example in Table 5, below.

According to this further species of the second embodiment of theinvention, the smallest output values are no longer formed by drivingindividual electrodes, but by subtraction between at least two largerelectrodes.

The value range, covered in a linear form, thus varies onlyinsignificantly. However, the size ratio between the smallest andlargest electrode is now only 5:1029=1:206, as can be seen, e.g., fromTable 5. TABLE 5 Value sequence with the approach based on Equation 4with a modified LSB triple (see FIG. 1) Position Value a₀ 5 b₀ 6 c₀ −11a₁ 7 b₁ 14 c₁ −21 a₂ 49 b₂ 98 c₂ −147 a₃ 343 b₃ 686 c₃ −1029For the length ratios of the electrodes of the larger electrode triples(i.e., from the second least significant electrode triple), the smallestelectrode a_(x) is once again calculated, from Equation (4), as:$a_{x} = {\left( {\sum\limits_{i = 0}^{x}\left( {\sum\limits_{j = 0}^{2}{l_{i,j}}} \right)} \right) + 1}$The length of the central electrode b_(x) is twice that of a_(x), i.e.,b_(x)=2 a_(x). The greatest electrode length c_(x) within a triple isgiven by the sum of a_(x) and b_(x), i.e., c_(x)=a_(x)+b_(x). Theelectrodes in the lowest triple are lengthened by precisely “5”primarily because the length ratio (^(˜)1:206) achieved in this way iswithin a range that can be well managed.

Fundamentally, this improvement to the production capability of theelectrode structure sought is subject to the following considerations:the triple structure (c=a+b) should be retained in the design, and theresultant output characteristic should have no discontinuities in thecentral area. The latter requires that the values 0, ±1, ±2 . . . can beproduced.

The smallest value that can be produced by the triple above the lowesttriple is ±7 in the example shown in Table 5. The values from 1 to 6must therefore be generated by connection of the lower triple. The −1,for example, is formed as the sum of the 6, the 14 and −21.

As a general statement, it is necessary that:

-   -   all the values from 1 to 6 can be constructed by addition or        subtraction between up to two electrodes in the lowest triple        and the magnitude of an electrode in the next triple, or zero.    -   no electrode weighting is carried out twice.

The generalization of the constraints for lengthening the electrodes inthe lowest triple is:

The new electrode length l′_(ij) can be produced by a combination of apreviously chosen electrode length and the length of an electrode inanother triple (linear combination)l _(i,j) =±l _(i,j) ′±l _(k,l) wherei≠k  (Equation 5)

The index “i” again denotes the triple number {1, 2, 3 . . . }, whilethe index “j” denotes the number of the electrode in the respectivetriple {0, 1, 2}. Analogous to “i”, the index “k” denotes a triplenumber. It is the number of the triple from which the second electrodelength can be taken. In addition, the new lengths must once againsatisfy the condition a+b=(−)c. If this condition is not satisfied, thenthe length of the longest electrode (l_(3,2)) in the lowest third mustbe adapted by the appropriate difference in accordance with thefollowing relationship: $\begin{matrix}{l_{3,2}^{\prime} = {l_{3,2} + \left( {\sum\limits_{j = 0}^{2}l_{0,j}^{\prime}} \right)}} & \left( {{Equation}\quad 6} \right)\end{matrix}$This allows the following exemplary combinations to be represented forthe lowest triple:

-   -   1, 2, −3 (Output distribution: Table 4)    -   2, 4, −6    -   2, 8, −10    -   3, 5, −8    -   3, 6, −9    -   5, 6, −11 (Table 5)    -   5, 10, −15    -   6, 10, −16    -   6, 12, −18    -   8, 9, −17.

In the last example, the electrode with value a₀ is already larger thanthe smallest electrode of the following triple. Thus any furtherlengthening of the lower triple with respect to reduction of the lengthratios does not provide any further advantage.

The “5” was chosen as the start value in Table 5—as alreadydescribed—due to the fact that the length ratio of the longest electrodeto the shortest electrode has been sufficiently reduced. Furthermore,this combination can be easily produced by constant increase in theoriginal lengths of the values of a₀ and b₀ (from Table 4).

As can be seen, in principle, the elementary triple structure of thefirst described embodiment applies to the second fundamental embodimentof the invention, with the length ratios being converted to binary formfrom the second electrode triple. The size of the area covered linearlyby a basic step width (for example |1|) extends from −1192 to +1194.Once again, the resolution is (approximately) 11 bits.

If binary signal processing is intended to be provided within the driveelectronics for a phase modulator according to the invention (generallythe case), a non-binary phase modulator according to the invention canbe used with the aid of a correction table that converts the calculateddigital values to non-binary values. The correction table can bedesigned to be programmable in memory. In addition to the conversionfrom binary to non-binary values, it can also correctproduction-dependent, or operation-dependent faults and errors in thephase modulator. FIG. 3 illustrates the basic circuit design. The binaryvalues that correspond to a specific phase value are supplied from acontrol device (controller) 30 to a conversion or correction table 31.The table 31 controls a downstream switch 32 through which theindividual electrodes E0 to E11 of the phase modulator 33 are drivenwith a signal combination that corresponds to the non-binary value.

The modified embodiment of the conversion and correction circuit shownin FIG. 4 allows an external signal to be supplied to the correctiontable, (e.g. a temperature signal or a signal which takes account ofage-dependent changes, as a readjustment correction).

The illustrated example of the conversion and correction circuit shownin FIG. 5 has two or more, (e.g. four), correction tables KT1 to KT4.These may be integrated in an ASIC and likewise make it possible to usean optimized correction table in each case as a function of an externalsignal.

The invention thus provides a digital phase modulator with considerablyincreased resolution without requiring an excessive length ratio (e.g.one that corresponds to a value of 1:2¹¹).

FIG. 2 illustrates a specific exemplary embodiment of the inventionrelating to the MIOC of a fiber-optic gyroscope with a closed controlloop. After a splitter 22 (Y splitter), two parallel light guidancepaths L1, L2 run in the substrate of an MIOC 20 for the forward andbackward paths of a polarized light wave. The light wave passes throughthe measurement coil of an FOG and is acted on by a digital phasemodulator with a parallel double configuration of the same phase, butthe opposite mathematical sign, on the forward and backward paths. Thephase modulator, which is in the form of a parallel double version, is,according to the invention, split into four electrode triples. These areannotated with the reference numbers 1 to 4 as in FIG. 1. The driveconnections for the electrodes are provided along the lower edge of theMIOC substrate in FIG. 2, and are annotated E0 to E11 in a mannercorresponding to FIG. 1. The overall length of this phase modulatorarrangement on the MIOC chip is, for example, about 10 mm.

It is particularly advantageous for the two shorter electrodes E0, E1 inthe first low significance (LSB) triple to have the respective lengthvalues a₁=|5| and b₁ |6|, and, for the longest electrode (E2) of thistriple to have the length value c₁=|11|. At the same time, the lengthratio ν for the electrode lengths (a₂ to c₄) of all the other, moresignificant electrodes E3 to E11 is: $\begin{matrix}{\nu = {\frac{1}{2} + {\sqrt{\frac{5}{4}}{1.618.}}}} & \left( {{Equation}\quad 3} \right)\end{matrix}$

If a phase modulator according to the invention is intended to beoperated with binary values, an electronic correction table can beemployed for conversion of binary phase values to the non-binary drivevalues for the electrodes. Such correction table may be programmable inmemory. In particular, it may also contain correction values forcorrection of production-dependent and/or operation-dependent faults anderrors in the phase modulator. It may also be advantageous to provide atleast two differently programmed correction tables, between which it ispossible to switch by means of a control device, as a function of anexternal parameter, (e.g. temperature).

While this invention has been described with reference to itspresently-preferred embodiment, it is not limited thereto. Rather, theinvention is limited only insofar as it is defined by the following setof patent claims and includes within its scope all equivalents thereof.

1. A digital phase modulator for a fiber-optic signal transmission or measurement device, which has a predetermined total number of electrodes of different length which are arranged parallel and on both sides of a light guidance path in or on an optical substrate, in which case preferably identical control potentials can be applied to the electrodes on both sides of the light guidance path, in such a way that a large number of phase values for a light wave which is running on the light guidance path can be set by changing the drive selection of electrode combinations within a predetermined value range, characterized in that the electrodes are arranged in two or more triples along the light guidance path, with in each case two electrodes of successive length within a triple having the same length ratio with respect to one another.
 2. The phase modulator as claimed in claim 1, characterized in that the respective longest electrode in a triple is arranged on one side of the light guidance path and the two other shorter electrodes are arranged along the other side of the light guidance path, on or in the substrate.
 3. The phase modulator as claimed in claim 1, characterized in that the length ratio is: $\nu = {\frac{1}{2} + {\sqrt{\frac{5}{4}}{1.618.}}}$
 4. A digital phase modulator for a fiber-optic signal transmission or measurement device, which has a predetermined total number of electrodes of different length which are arranged parallel and on both sides of a light guidance path in or on an optical substrate, in which case preferably identical control potentials can be applied to the electrodes on both sides of the light guidance path, in such a way that a large number of phase values for a light wave which is running on the light guidance path can be set by changing the drive selection of electrode combinations within a predetermined value range, characterized in that the electrodes are arranged in two or more triples along the light guidance path, with the longest electrodes of successive triples having the same length ratio with respect to one another from the second to the most significant triple, the electrode length ratios of the electrode triples above the first low significance triple being defined such that the length of the respectively shortest electrode value is: $a_{x} = {l_{x,0} = {{\left( {\sum\limits_{i = 0}^{x - 1}\left( {\sum\limits_{j = 0}^{2}{l_{i,j}}} \right)} \right) + {1\quad{for}\quad x}} \in \left\{ {1,2,3} \right\}}}$ where the index “I” denotes the triple number and the indes “j” indicates the number of the respective electrode in the triple, and the length of the respective central electrode is governed by the relationship b_(x)=2a_(x), and the length of the respectively longest electrode is given by the relationship c_(x)=a_(x)+b_(x), and the electrode lengths of the first, least significant triple being chosen such that the smallest step widths of the light phase in the output value range of the phase modulator can be formed by subtraction between the associated phase values of at least two larger electrodes, and in order to reduce the length ratio of the longest to the shortest electrode in the modulator in the lowest triple, its electrodes are relatively lengthened such that an additive combination of the values of the two shorter electrodes results in the length value of the longest electrode in this lowest triple.
 5. The phase modulator as claimed in claim 4, characterized in that the respectively longest electrode in a triple is arranged on one side of the light guidance path, and the two other, shorter electrodes are arranged on the other side of the light guidance path, and in that the sum of the lengths of the two shorter electrodes is equal to the length of the longest electrode.
 6. The phase modulator as claimed in claim 5, characterized in that the electrode length ratios of the electrode triples above the lowest triple are defined such that the length (l_(x,o)) of the respectively shortest electrode value (a_(X)) is: $a_{x} = {l_{x,0} = {{\left( {\sum\limits_{i = 0}^{x - 1}\left( {\sum\limits_{j = 0}^{2}{l_{i,j}}} \right)} \right) + {1\quad{for}\quad x}} \in \left\{ {1,2,3} \right\}}}$ where the index “i” denotes the triple number {0, 1, 2, 3 . . . }, and the index “j” indicates the number of the respective electrode in the triple {0, 1, 2}, and the length (b_(X)) of the respective central electrode is governed by the relationship b_(X)=2a_(x), and the length (c_(X)) of the respectively longest electrode is given by the relationship c_(X)=a_(x)+b_(X), and in that the electrodes in the lowest (first) triple are lengthened such that an additive combination of the values of the two shorter electrodes (E₀, E₁) results in the length value of the longest electrode (E2) in this lowest triple.
 7. The phase modulator as claimed in claim 4, characterized in that the two shorter electrodes in the lowest triple have the respective length values a₀=|5| and b₀=|6| and the longest electrode (E₂) in this triple the length value c₀=|11|.
 8. The phase modulator as claimed in claim 4, characterized in that the two shorter electrodes in the lowest triple have the respective length values a₀=|2| and b₀=|4| and the longest electrode (E₂) in this triple the length value c₀=|6|.
 9. The phase modulator as claimed in claim 4, characterized in that the two shorter electrodes in the lowest triple have the respective length values a₀=|2| and b₀=|8| and the longest electrode (E₂) in this triple the length value c₀=|10|.
 10. The phase modulator as claimed in claim 4, characterized in that the two shorter electrodes in the lowest triple have the respective length values a₀=|3| and b₀=|5| and the longest electrode (E₂) in this triple the length value c₀=|8|.
 11. The phase modulator as claimed in claim 4, characterized in that the two shorter electrodes in the lowest triple have the respective length values a₀=|3| and b₀=|6| and the longest electrode (E₂) in this triple has the length value c₀=|9|.
 12. The phase modulator as claimed in claim 4, characterized in that the two shorter electrodes in the lowest triple have the respective length values a₀=|5| and b₀=|10| and the longest electrode (E₂) in this triple has the length value c₀=|15|.
 13. The phase modulator as claimed in claim 4, characterized in that the two shorter electrodes in the lowest triple have the respective length values a₀=|6| and b₀=|10| and the longest electrode (E₂) in this triple has the length value c₀=|16|.
 14. The phase modulator as claimed in claim 4, characterized in that the two shorter electrodes in the lowest triple have the respective length values a₀=|6| and b₀=|12| and the longest electrode (E₂) in this triple has the length value c₀=|18|.
 15. The phase modulator as claimed in claim 4, characterized in that the two shorter electrodes in the lowest triple have the respective length values a₀=|8| and b₀=|9| and the longest electrode (E₂) in this triple has the length value c₀=|17|.
 16. The phase modulator as claimed in claim 8, characterized by an electronic correction table, which is associated with the phase modulator, for conversion of binary phase values to nonbinary drive values for the electrodes.
 17. The phase modulator as claimed in claim 16, characterized in that the correction table is designed to be programmable in memory.
 18. The phase modulator as claimed in claim 9, characterized in that, in addition to binary/nonbinary conversion, the correction table contains correction values for correction of production-dependent and/or operation-dependent faults and errors in the phase modulator.
 19. The phase modulator as claimed in claim 10, characterized in that at least two differently programmed correction tables are provided, between which it is possible to switch by means of a control device, as a function of an external parameter.
 20. The phase modulator as claimed in claim 11, characterized in that the external parameter is the temperature.
 21. The phase modulator as claimed in claim 1, characterized by an electronic correction table, which is associated with the phase modulator, for conversion of binary phase values to nonbinary drive values for the electrodes 